1. Field
A sheet feed mechanism is provided.
2. Related Art
As illustrated in FIG. 3, a conventional sheet feed mechanism 30 includes a rotatable pressure contact roller 32 and a sheet feed roller 31 that is driven to rotate. The sheet feed roller 31 and the pressure contact roller 32, which are each formed into a longitudinal shape, can nip a recording sheet 33 in pressure contact therebetween. The recording sheet 33 is a heavy paper, such as a photographic paper. When the sheet feed roller 31 is rotated in a clockwise direction (i.e., a direction indicated by an arrow), the recording sheet 33 can be conveyed downward in the figure.
One end in a longitudinal direction of the pressure contact roller 32 is provided with an actuating arm 34 that serves as a pressure contact release mechanism for releasing the pressure contact of the pressure contact roller 32 with the sheet feed roller 31.
In the actuating arm 34, a spindle 34a located at a lower position in the figure serves as a fulcrum, and an upper portion of the actuating arm 34 in the figure can be rotated. An approximately intermediate portion of the actuating arm 34 is resiliently biased by a first resilient member 35 that is formed by a coil spring. Therefore, the pressure contact roller 32 is caused to be in pressure contact with the sheet feed roller 31 due to biasing force of the first resilient member 35.
A motor 36 formed by a stepping motor is provided as a member for driving to rotate the actuating arm 34. A crank arm 37 is axially fastened to a drive shaft 36a of the motor 36, and a second resilient member 38 formed by a coil spring is connected between a leading end of the crank arm 37 and the actuating arm 34.
In the thus configured conventional sheet feed mechanism 30, the motor 36 is driven to rotate by a predetermined angle, with the recording sheet 33 fed between the sheet feed roller 31 and the pressure contact roller 32. Thereby, as illustrated in FIG. 3, the crank arm 37 is moved to an approximately horizontal position in the left-pointing direction in the figure.
The biasing force of the first resilient member 35 becomes larger than the biasing force of the second resilient member 38, and the pressure contact roller 32 nips the recording sheet 33 in pressure contact with the sheet feed roller 31.
The sheet feed roller 31 is driven to rotate in the clockwise direction, and the recording sheet 33 is conveyed downward in the figure.
To release the pressure contact of the pressure contact roller 32 with the sheet feed roller 31 in accordance with need, the crank arm 37 drives to rotate the motor 36, which has been in an approximately horizontal position in the left-pointing direction in the figure, by an approximately 180 degrees. Thereby, the crank arm 37 is moved to an approximately horizontal position in the right-pointing direction in the figure.
The resilient force of the second resilient member 38 becomes larger than the resilient force of the first resilient member 35, and the pressure contact roller 32 oscillates in the right direction in the figure, with the spindle 34a of the actuating arm 34 functioning as the fulcrum. The pressure contact roller 32 is separated from the sheet feed roller 31. The conventional sheet feed mechanism of this type is described in Japanese Unexamined Patent Application Publication No. 2000-321680, for example.
In the conventional sheet feed mechanism 30 as described above, however, the actuating arm 34 attached to the one end of the longitudinally-shaped pressure contact roller 32 is rotated to cause the pressure contact roller 32 to contact and separate from the sheet feed roller 31. Therefore, the pressure contact roller 32 tends to be obliquely positioned, and it is difficult to perform and release the pressure contact of the pressure contact roller 32 parallel to the recording sheet 33.
A deviation in timing occurs in performing and releasing the pressure contact of the pressure contact roller 32 with respect to the recording sheet 33 in the longitudinal direction. This may cause a conveyance skew or the like in the recording sheet 33 in a conveyance process, and thus may cause such phenomena as oblique conveyance (i.e., oblique passage) of the recording sheet 33.